다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

X-ray analysis of ZnO nanoparticles by Williamson–Hall and size–strain plot methods

ZnO nanoparticles were prepared by coprecipitation method at 450C. X-ray diffraction result indicates that the sample is having a crystalline wurtzite phase. Transmission electron microscopy (TEM) result reveals that the ZnO sample is spherical in shape with an average grain size of about 50nm. X-ray peak broadening analysis was used to evaluate the crystalline sizes and lattice strain by the Williamson-Hall (W-H) analysis. All other relevant physical parameters such as strain, stress, and energy density values were also calculated using W-H analysis with different models, viz, uniform deformation model, uniform deformation stress model and uniform deformation energy density model. The root mean square strain was determined from the interplanar spacing and strain estimated from the three models. The three models yield different strain values; it may be due to the anisotropic nature of the material. The mean particle size of ZnO nanoparticles estimated from TEM analysis, Scherrers formula and W-H analysis is highly intercorrelated.

/pdf/williamson-hall-analysis-in-estimation-of-lattice-strain-in-1epz6r1apj.pdf

Williamson-Hall analysis in estimation of lattice strain in nanometer-sized ZnO particles

The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Intrinsic ripples in graphene

Welding Metallurgy of

The work hardening effect of the shot peening affected layer of hardened and low temperature tempered spring steel was investigated using the method for determining the yield strength of a metallic surface with biaxial residual stress. The results show that for the surface layer of the specimens, the microhardness and half-width values of X-ray diffraction lines is decreased, whereas the yield strength is increased during shot peening. Thus, shot peening leads the surface layer of steel in hard state to work hardening instead of work softening.

An Investigation into Work Hardening of Shot Peening Affected Layer Using X-Ray Stress Analysis Technique

The advance of the XRD technique allows us to reach the properties of each coarse grain. This paper has demonstrated a new method to determine stress in a single crystal for multicrystal material and this new method could be specially applied for any symmetric crystalline systems. The strain tensor e is determined by the change of the metric tensor G before the initial state and after the deformed state in the crystal reference system. Then stress tensor at grain scale is calculated by the Hooks law. The stress evaluations are carried out in coarse grains of a thin galvanized coating on a steel substrate during tensile loading. This study allows us to link the microstructure evolution to the elastic heterogeneity at grain scale or between the grains.

Stresses analysis on coarse grain Zn film during tensile loading

Vacancy diffusion in Cu Σ = 9 [110] twist grain boundary

It has been shown that Al–Li alloys exhibit improved mechanical properties at low temperatures in comparison with at room temperature (RT) [1, 2]. As a result, the alloys have great potential value for cryogenic application with their low density and high elastic modulus, but the mechanisms of the property improvement at low temperatures are not yet well understood. Generally, the probable mechanisms are as follows [3, 4]:

The cryogenic properties of Al-Li single crystals

The monolayer (ML) and submonolayer Pt on both terminations of PbTiO3(110) polar surface have been studied by using density functional theory (DFT) with projector-augmented wave(PAW) potential and a supercell approach. The most favored ML Pt arrangements on PbTiO and O2 terminations are the hollow site and the short-bridge site, respectively. By examining the geometries of different ML arrangements, we know that the dominant impetus for stability of the favored adsorption site for PbTiO termination is the Pt–Ti interaction (mainly from covalent bonding), while that for O2 termination is the Pt–O interaction (mainly from ionic bonding). In addition, the appearance of the gap electronic states in the outermost layers of each termination indicates that a channel for charge transfer between adsorbed layer and substrate is formed. Moreover, the interface hybridization between Pt 5d and O 2p orbitals is also observed, especially for ML Pt on O2 termination. The stability sequences for various arrangements of 1/2 ML Pt adsorption conform well with those of ML Pt adsorption, and the most stable arrangement is energetically more favorable than the corresponding ML coverage in the view of adsorption energy maximization. The behavior, i.e. the increase in adsorption energy with decrease in coverage, indicates that PtPt interactions weaken those between Pt and the substrate. Copyright © 2009 John Wiley & Sons, Ltd.

Vincent Ji

Papers

An Investigation into Work Hardening of Shot Peening Affected Layer Using X-Ray Stress Analysis Technique

Stresses analysis on coarse grain Zn film during tensile loading

Vacancy diffusion in Cu Σ = 9 [110] twist grain boundary

The cryogenic properties of Al-Li single crystals

Pt adsorption on the PbTiO3(110) polar surface: a density functional theory study